The Warren Court's decision about prayer in public schools outlawed official prayers in public schools. It happened because official praying in public schools its considered a unconstitutional action, violating the the First Amendment of U.S Constitution that guarantees the U.S citizens, on summary, freedom of religion, speech, press and association.
The Engel v. Vitale (1962) case has made public the issue concerning the recommendation, made in 1951 by State Board of Regents from New York to New York's public schools with the purpose of "Statement on Moral and Spiritual Training in Schools", that encouraged daily reciting of prayers, during the morning. Though the prayers were not mandatory and considered denominational neutral, it still violated the excerpt of the Constitution that stated "Congress should make no law respecting an establishment of religion", because official praying itself its considered a religious activity. Thus the outcome of the case was that State officials (such as the State Board of Regents) could not compose or incite the recitation of prayers in schools.